The subject invention pertains to the field of agriculture, more particularly to the biocontrol of undesirable plant species.
Tropical soda apple (Solanum viarum Dunal; TSA) is a prickly perennial weed species indigenous to South America. Introduced into Florida in 1988 it has since become one of the most serious invasive weeds in the southeastern United States (Mullahey, 1996). Tropical soda apple is designated a noxious weed under the Federal Noxious Weed Statutes. It proliferates rapidly by both sexual and asexual means. TSA is dispersed by cattle, birds, wild animals, and certain ranching and agricultural practices. In addition to being a highly competitive weed, TSA poses an additional threat as a reservoir for several economically important plant viruses (McGovern et al., 1994). TSA is currently managed by a combination of mowing and application of the chemical herbicide triclopyr (Remedy(copyright)) (Akanda et al., 1997), but alternative means of control are necessary and desirable.
All references cited herein are incorporated by reference in their entirety, to the extent not inconsistent with the explicit teachings set forth herein.
As an alternative to chemical herbicides, we searched for a suitable pathogen of tropical soda apple (TSA) for development as a bioherbicide and have discovered that Tobacco mild green mosaic virus (TMGMV) induces a lethal, systemic, hypersensitive response in TSA. TMGMV is a member of the tobamoviruses, which consist of mechanically transmitted, rod-shaped, RNA viruses that are strictly plant pathogens. The type species of Tobamovirus is Tobacco mosaic virus U1 (TMV U1), a widely distributed plant virus. Unlike TMGMV, TMV U1 and Tomato mosaic virus (ToMV, another Tobamovirus species), caused only mild, nonlethal mosaic or mottling of the TSA leaves. The atypical lethal effect of TMGMV on TSA was unexpected and is previously unknown. Also unknown was the feasibility to use TMGMV as a biocontrol for TSA.
Tropical soda apple serves as a host for TMV U1, ToMV, and TMGMV. In contrast to the mild, systemic mosaic symptoms caused by TMV U1 and ToMV, TMGMV causes rapid death of TSA. This death occurs due to a massive, systemic, hypersensitive plant response to infection by the virus. Both serological and molecular evidence confirm that TMGMV is responsible for the rapid and high rate of mortality on TSA. The age of TSA at the time of TMGMV inoculation does not affect the mortality rates, but the first expression of symptoms and first plant mortality are slightly delayed in older plants as compared to younger plants. Thus, the ability to control TSA by TMGMV is not limited by plant age. Temperature is usually not a limiting factor, although disease development will be slowed or prevented if the inoculated TSA plants are maintained continuously at 32xc2x0 C. (or presumably at higher temperatures). However, under normal field conditions, a diurnal temperature fluctuation will occur and as our results indicate, TMGMV kills TSA plants under the diurnal cycle of 32/22xc2x0 C. temperatures. To avoid possible adverse effects of high temperatures according to the subject invention, the TMGMV is preferably used in the field during the cooler months of spring and fall.
The host reaction of two C. annuum cultivars indicates that, as a precaution, TMGMV should not be used in the vicinity of pepper crops. However, it is safe to use the virus near tomato and eggplant crops.
Field trials from Hawthorne (north-central Florida) and Deseret Ranch (south-central Florida) sites confirm the excellent efficacy of TMGMV as a biological control agent for TSA. The high temperature-induced, attenuated disease symptoms, seen in plants incubated at 32xc2x0 C., did not occur at either field site. Furthermore, the levels of TSA control obtained with TMGMV were comparable to the control levels obtained with chemical herbicides, but without the risks of chemical contamination.
Other advantages of TMGMV are first, the feasibility to produce abundant supplies of the virus by a simple, inexpensive method in susceptible tobacco; and second, the extremely small doses needed for high levels of TSA control. This virus-based bioherbicide system can be produced, developed, and registered more easily than fungal-based bioherbicides. Another important aspect of the TSA-TMGMV system is its highly novel mode of action, which is based on a systemic hypersensitive host response triggered by a gene of the virus.
Accordingly, it is an object of the present invention to provide a novel method of weed control.
It is a further object of the present invention to provide a method of weed control utilizing tobomoviruses.
It is a still further object of the present invention to provide a method of weed control utilizing TMGMV.
It is a still further object of the present invention to provide a method of controlling the tropical soda apple utilizing TMGMV.
Further objects and advantages of the present invention will become apparent by reference to the following detailed disclosure of the invention and appended photographs.